Italian structural monitoring regulations: NTC 2018, MIT Guidelines 2020 and the compliance plan

Italian regulations on structural monitoring of bridges consist of several texts that together create a comprehensive framework of obligations to consider when designing a monitoring plan. The key laws are: Chapters 8 and 9 of the NTC 2018 (Ministerial Decree of January 17, 2018) for interventions on existing structures and static load testing, the MIT Guidelines approved by the General Assembly of the Consiglio Superiore dei Lavori Pubblici with opinion no. 88/2019 dated April 17, 2020 and made mandatory by MIT Decree no. 578 of December 17, 2020 for existing bridges, and NTC Circular no. 7 of January 21, 2019 for operational interpretation.

Two regulatory levels

The NTC 2018 is the general code for all structures. Chapter 9 establishes that, within the scope of static load testing, the testing engineer may require scheduled monitoring of significant parameters of the structure's behavior, to be continued after testing if necessary.

Chapter 8 governs interventions on existing structures, including strengthening and upgrading, and requires investigations and inspections aimed at characterizing the condition of the structure.

The 2019 Circular clarifies that these are surveys aimed at verifying the structure's behavior during specific phases rather than a continuous obligation on structures in service.

The NTC 2018 covers load testing (a point-in-time event) and interventions (extraordinary events), but does not address the "ordinary life" of the structure, and therefore does not mandate continuous structural monitoring. This gap was filled by the MIT Guidelines 2020, which specify the requirements in this area.

Structural monitoring is required for structures that exceed a defined risk threshold. However, it is important to clarify the temporal scope: Decree 578/2020 initially applied only to roads managed by ANAS S.p.A. and motorway concessionaires. The extension to local authorities (municipalities, provinces, regions) came with Decree no. 204 of July 1, 2022, which involved these entities in the pilot implementation of the Guidelines on their own road networks.

It should be noted that Decree 204 did not impose an obligation identical to that of ANAS and concessionaires, but established a pilot regime in which the relevant authorities were required to propose, by December 22, 2022, the road sections containing bridges and viaducts to be included in the pilot program.

Why these guidelines exist

On August 14, 2018, the Polcevera viaduct in Genoa, also known as the Morandi Bridge, collapsed killing 43 people. The investigations made it clear that Italy had no uniform method for assessing existing bridges. Each operator used its own criteria, its own inspection frequencies and its own intervention thresholds, meaning there was no solid, tested reference standard. The NTC, whose ministerial decree had been signed about seven months earlier, did not cover the ordinary operation of existing structures.

The Consiglio Superiore dei Lavori Pubblici approved the Guidelines with opinion no. 88/2019 of the General Assembly, dated April 17, 2020. MIT Decree no. 578 of December 17, 2020 made them mandatory for infrastructure managed by ANAS and motorway concessionaires. Decree no. 204 of July 1, 2022 extended the pilot program to local authorities, involving municipalities, provinces and regions for the first time. A subsequent MIT decree of December 9, 2024 extended the pilot period deadline to December 29, 2026.

A six-level mechanism

The six levels established by the Guidelines function in practice as a triage system: all structures are examined, but in-depth analysis resources are concentrated where the risk justifies them.

Level 0 is the registry census: location, typology, materials, year of construction, operator and average traffic. For many municipalities, this is the first time their bridge inventory is systematically catalogued, integrating documentation often scattered across different offices.

Level 1 is the on-site visual inspection, conducted by a qualified engineer with a standardized form covering the condition of the concrete, reinforcement corrosion, the state of bearings and expansion joints, and pier erosion. Photographic documentation is mandatory.

Level 2 is where the Attention Class is assigned, combining four independent risk dimensions (structural-foundational, seismic, landslide and hydraulic), each calculated as hazard times vulnerability times exposure. Each dimension produces a partial attention class; the overall class is determined by combining the partial classes according to specific rules defined in the Guidelines. There are five classes: Low, Medium Low, Medium, Medium High, High. Structures classified as Low and Medium Low remain under periodic visual surveillance and do not require further levels, while maintaining inspection and scheduled maintenance obligations. The Medium, Medium High and High classes proceed to Level 3.

Level 3 is a mandatory preliminary assessment for the Medium and Medium High classes, aimed at determining whether Level 4 investigations are needed. For the Medium class, Level 3 may conclude without further steps if the preliminary assessment does not identify critical issues. For the High class, the path typically leads directly to the in-depth verifications of Level 4, where Level 3 tends to merge with the next level rather than constituting a standalone step.

Level 4 involves detailed safety verifications and material testing. It is mandatory for the High class and may also be required for other classes following Level 3.

Level 5 is different in nature from the previous levels, as it does not concern the individual structure but the interaction between the bridge and the road network it belongs to. It applies to bridges of significant relevance to the transport network and involves transport system resilience analysis, assessing the socio-economic consequences of a potential service interruption. The Guidelines do not detail the operational procedures for Level 5, referring instead to internationally recognized authoritative documents. This generic reference actually leaves a significant operational gap, as no specific documents are cited.

It is worth emphasizing that the Attention Class is a composite concept and is not limited to the condition of the structure alone. For example, a bridge in good structural condition but located over a watercourse with high hydraulic hazard and carrying heavy traffic can reach Medium High on exposure and hazard alone — no defects in the bridge's concrete are needed for it to be classified in a higher class.

Surveillance and monitoring

The Guidelines use two terms with distinct operational meanings: structural monitoring and surveillance.

Surveillance is periodic visual inspection conducted by qualified personnel, with intervals defined by the surveillance plan based on the Attention Class. It applies to all bridges regardless of risk and does not involve the installation of permanent hardware.

Structural monitoring, on the other hand, is the acquisition of data through sensors installed on the structure. The Guidelines distinguish two modes: periodic monitoring, based on measurement campaigns at defined intervals, and continuous monitoring, with uninterrupted data acquisition and preset alarm thresholds. The Attention Class and the specific characteristics of the structure determine which option to choose. Structural monitoring applies in particular to structures in the Medium High and High classes.

Structural monitoring is covered in Part 3 of the Guidelines, which is a structurally separate section from the six classification and assessment levels, while being functionally connected to them. The Level 2 classification, specifically the Attention Class, determines whether structural monitoring is required.

To put things in perspective: in a portfolio of 20 bridges managed by a municipality, a classification identifying 3 structures as Medium High produces a specific operational scope. Periodic surveillance on all 20, structural monitoring on the 3 critical ones. A site visit program, however thorough, does not replace a sensor system when the regulations require one.

Prestressed concrete: special investigations

A significant share of Italian bridges built in the 1960s and 1970s uses prestressed concrete, a technique that encloses prestressing tendons within the cross-section. The Guidelines require investigations for these structures that go well beyond visual inspection: ground-penetrating radar (GPR) surveys to locate the arrangement of prestressing tendons, ultrasonic testing to detect discontinuities, endoscopic inspections to verify the condition of grout injections, and tomographic investigations to reconstruct the internal cross-section. For municipalities with bridges from that era, these special investigations fall within Levels 3 and 4, meaning the assessment and verification phases that follow risk classification.

Environmental data becomes a requirement

Both the NTC 2018 and the MIT Guidelines 2020 require that structural measurements be interpreted by isolating the signal from environmental effects. The Guidelines specify that modal frequencies and slow drift must be reported using methodology that isolates the structural signal from environmental effects.

On a typical concrete bridge, the international technical literature documents that seasonal thermal variations produce modal frequency variations in the range of 2–10%. In practice, these are almost always larger than the signature of actual damage. Therefore, temperature and humidity must be recorded in parallel, so that the system can distinguish a hot day from an incipient loss of stiffness.

As a result, a monitoring plan must include environmental sensors.

How long the process takes

The path from Level 0 to an active system takes more than a few weeks, because each step toward compliance requires the involvement of various professionals:

• The census requires document recovery and preliminary site visits.
• Visual inspections depend on the availability of qualified engineers, a market concentrated around the same deadline window.
• Risk classification requires cross-referencing inspection data with seismic, hydrogeological and hydraulic hazard layers for the territory (ISPRA data, river basin authorities, seismic maps).
• For structures classified as Medium High or High, what follows is the design of the measurement chain, procurement of the installation, and commissioning of the system. In parallel, the reporting workflow to ANSFISA must be activated.

Each step involves different parties: the municipal technical office, external professionals registered with the professional order, the sensor provider, and possibly a monitoring company. The documentation produced through the involvement of all these people is ultimately what constitutes compliance. The documents include census forms, visual inspection reports, risk classification reports, the structural monitoring plan, and periodic reports of measured data.

Reporting obligations to ANSFISA

Monitoring data must be archived, accessible and transmittable to ANSFISA (Agenzia Nazionale per la Sicurezza delle Ferrovie e delle Infrastrutture Stradali e Autostradali — the National Agency for Railway and Road Infrastructure Safety). For the practical implementation of the Guidelines, ANSFISA has published its own Operational Instructions, which constitute an essential reference for operators. These instructions define data transmission procedures, required formats and update timelines.

The system must produce structured reports with processed, readable data. This data processing becomes unmanageable for a municipality managing 10 or 20 bridges. This is why SHM (Structural Health Monitoring) platforms exist that aggregate data from multiple structures into a single dashboard, with automatic report generation and alarm thresholds configured by Attention Class for each structure.

What changes after the pilot period

When the pilot period closes, the Guidelines operate under ordinary regime. Risk classification becomes a recurring activity, because the condition of structures evolves and the environmental hazard framework gets updated. Monitoring of critical bridges becomes a permanent function of the managing authority, with the prospect of being integrated into ordinary public works planning. This is a desirable connection, even though the Guidelines do not establish a direct link with the three-year public works programming under the Codice dei contratti (Public Contracts Code).

The time series collected between 2025 and 2026 represent the first uniform national database on Italian bridges. Their value will depend on how managing authorities use this data in subsequent planning cycles: whether it enters three-year plans as a priority parameter or remains in archives as compliance documentation.

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